Thanks for your wonderful post. I enjoy hearing your perspective on Taijiquan, especially since we have differing backgrounds and perspectives.

I enjoy reading your perspectives as well.

In my experience, the concepts of the circle and the square have not been clearly explained. But I think that many of these concepts are interrelated (empty/full, excess/deficiency, resisting/losing, etc.). I would like to hear more about how you understand ‘seek the straight in the curve,’ especially since you do not seem to focus on roundness and squareness (the circle and the square, the curved and the straight, the round and the flat); I consider them to be interrelated concepts.

I have been taught about squares and circles, but do not recall much discussion that matches the sense of the text under discussion.

I view many concepts to be interrelated, it is not particularly easy to explain, but let me try a somewhat simplified explanation. If you have a properly inflated ball that is floating on water such that it can freely rotate in all directions (as well as being able to move along the water in any direction, plus possessing buoyancy allowing it to resist being pushed underwater), and you tried to control this ball with your finger, it would be very difficult to gain a point of application for your energy. The exception would be when the direction of your energy passes directly through the center of the ball (thus producing a line from the surface of the ball to its center, i.e. the straight in the curve). Any other angle of the energy of the finger would result in the ball deflecting your finger off of its intended direction (Lujin).

I agree with this thinking and do put it into practice. Although it can be called Lü, I would rather call the basic interaction Nian or "being sticky." Much of our training, however, stresses control and having two points of contact precisely to avoid this possibility of simple rotation. As a result, our concept of full and empty must go beyond round vs. square.

[Note, I do not have the video that you refer to, but I suspect that your specific examples of empty and full as well as double weighting, would be compatible with my understanding – we just tend to use different terminology and analogies...]

Almost all my "philosophizing" is linked to physical things that have been demonstrated on me or that I have demonstrated on others. I use this as a check on my speculation. If we had a physical reference, it would be easier to be sure we are talking about the same things.

Many of the applications where I think explicitly about full and empty are in situations where circles are not involved in the source of the change. In one counter I teach, the key is to wait out the opponent's fullness and movement and follow it to its limit. His emptiness and fullness must exchange over time, giving you a means to counter. In another, you wait out the opponent's emptiness with stillness until his emptiness must turn to fullness, again giving you an opportunity to counter. Sometimes it is the other way around.

In yet others, an application may work okay in an external way, but be dangerous to apply in a real situation without understanding the underlying requirements of full and empty. In some of these, you use two hands to control one of your opponent's arm and use the control of that arm to control the other arm. When I teach this, I explain that you must keep your opponent's arm full to keep his other arm empty and unable to strike you. You prolong the fullness of the arm under control beyond its usefulness. In another situation, where again you cannot intercept you opponent's technique, you may accelerate your opponent's cycle of empty to full, so that the fullness does not last long enough to be useful to him. In yet another, your opponent's palm may already be in contact with you and applying energy in away that does not allow you to deflect it. In that case, you may not form a convex curve, but rather a concave one in order to slightly rotate and change the nature of the opponent's contact from full to empty.

I would say that our thinking in these cases is more fundamental than circle versus square. It may be more pressure versus less pressure, right versus left, palm heel versus fingers, long versus short, sooner versus later, etc.

As for "seek the straight in the curve, I have various thoughts. In general, I think most of the Tai Chi sayings are meant to address specific issues. However, many of these sayings have general applicability and can be used in many ways. The trick is knowing when it is more useful to be specific and when it is more useful to be general.

I talk a lot about curves versus straight in my teaching and use it in my practice. I think the core meaning is to meet the opponent's straight energy with curves, store it, and then release it back in a straight line. From this I stress that in making curves you should understand the straightness that underlies it and vice versa. In Push, do not just think straighten the arm, but rather use the sphere implied by the arm shape to let straight energy spring out. In Rollback, do not just think of sending the opponent off in a straight line, but think of the underlying circle in your arms that creates the necessary tangent. Even in Cross Hands, do not just directly make a circle, but rather loosen up the joints and create the straight spokes that allow the universe to create the circle.

In many postures, we move from a circle with the palm facing one direction to the palm facing the other. I know three ways to do this. In rare case, we just bend at the elbow, but usually we do not. In one of these cases, we rotate the arm like a rolling pin while maintaining the same curve. In this case it is important to identify the axis of rotation. In the other, we straighten the arm in a very specific way to act as a bridge between the two curves. If you do not feel the axis or do not feel the straightness, you will not find the natural energy path and must work against the "groove" the universe provides.

If we try to make a straight line directly, we will always make errors and introduce imperfections, but if we do it indirectly and let the universe do it, the straight line will be perfect. If we try to make a circle arc by arc, we will introduce angles; however, if we use a straight line to do it and allow the universe to do the rest, the circle will again be perfect.